1. Field of the Invention
The present invention relates to a parking brake system. More particularly, the present invention relates to a parking brake system that uses a locking device that is prepared outside an automatic transmission to maintain a speed of the transmission.
2. Description of Related Art
Generally, as SBW (shift by wire) system transfers a demand of a driver to a TCU (transmission control unit) to release a parking condition through a hydraulic pressure, which is operated by a smaller force to provide comfort to a driver compared to a conventional TGS (transmission gear speed) lever (P/R/N/D).
If the hydraulic pressure of a piston member is deteriorated while the parking is released, the transmission can enter into a mechanical parking condition and therefore a locking device is to be prepared to prevent the mechanical parking.
In a conventional art, a locking device that is connected to a piston that is operated by hydraulic pressure of a transmission is prepared, to maintain the locking condition while the current is released. Accordingly, when the vehicle is stopped in an N (neutral) condition of a transmission, there is a problem that a battery can die.
That is, an NL (normal low) type of solenoid was used in a conventional art, and the NL type of solenoid valve maintains a locking condition while the current is being supplied thereto and releases the locking condition while the current is not supplied thereto.
In a conventional art, when a vehicle is stopped in an N speed, the transmission enters into a parking mode (P) speed. When the vehicle is stopped in an N speed and the NL type of solenoid valve is used to maintain the N speed, current is supplied to release a parking condition of the TCU, however, the current is to be continuously supplied to maintain the condition and therefore there is a problem that a battery can die.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.